Gill remodeling in response to hypoxia and temperature occurs in the hypoxia sensitive blunt snout bream (Megalobrama amblycephala)

In this study, we found that blunt snout bream (Megalobrama amblycephala) had a relatively high critical oxygen tension at which it lost its equilibrium (LOEcrit), confirming that it is a hypoxia sensitive fish. Blunt snout bream has the ability to remodel its gill structure in response to oxygen levels. When blunt snout bream were exposed to 4- or 7-days of hypoxia, the average protruding lamella heights and mean lamellar area of gills were significantly (P < 0.01) larger than those of normoxic controls. These changes resulted in reduced average interlamellar cell mass (ILCM) height and volume under hypoxia. After 1 week of normoxic recovery, gill lamellae were reversibly embedded with ILCM cells. Irrespective of dissolved oxygen concentration, the average protruding lamella height of fish gills at 25 °C was significantly (P < 0.01) larger than that of fish cultured at 10 °C, suggesting that blunt snout bream also have the ability to modify gill structure in response to water temperature. In response to hypoxia, blood erythrocyte count and haemoglobin (Hb) concentration increased significantly (P < 0.01) under hypoxia. Furthermore, the plasma chloride concentration ([Cl−]) was significantly (P < 0.01) reduced. Our results are the first to show that blunt snout bream, as a hypoxia sensitive fish, have the capacity to alter respiratory surface area in response to hypoxia and temperature.